Anthony Bruce Murphy
CSIRO, Manufacturing, Department Member
Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are... more
Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films.
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Cold atmospheric-pressure plasma (CAP) is a relatively new method being investigated for antimicrobial activity. However, the exact mode of action is still being explored. Here we report that CAP efficacy is directly correlated to... more
Cold atmospheric-pressure plasma (CAP) is a relatively new method being investigated for antimicrobial activity. However, the exact mode of action is still being explored. Here we report that CAP efficacy is directly correlated to bacterial cell wall thickness in several species. Biofilms of Gram positive Bacillus subtilis, possessing a 55.4 nm cell wall, showed the highest resistance to CAP, with less than one log10 reduction after 10 min treatment. In contrast, biofilms of Gram negative Pseudomonas aeruginosa, possessing only a 2.4 nm cell wall, were almost completely eradicated using the same treatment conditions. Planktonic cultures of Gram negative Pseudomonas libanensis also had a higher log10 reduction than Gram positive Staphylococcus epidermidis. Mixed species biofilms of P. aeruginosa and S. epidermidis showed a similar trend of Gram positive bacteria being more resistant to CAP treatment. However, when grown in co-culture, Gram negative P. aeruginosa was more resistant to...
A description of demixing that is mathematically simple and physically transparent is introduced. The dominant demixing process at high temperatures in an atmospheric-pressure nitrogen-argon arc is predicted to be that associated with... more
A description of demixing that is mathematically simple and physically transparent is introduced. The dominant demixing process at high temperatures in an atmospheric-pressure nitrogen-argon arc is predicted to be that associated with frictional forces. Spectroscopic measurments of the mass fraction distribution, which provide experimental confirmation of this demixing effect, are presented. It is shown that demixing can act to either increase or decrease the mass fraction of nitrogen as temperature increases, depending on the gas composition.
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ABSTRACT Although the LTE assumption is effective to evaluate high temperature region in the arc column in Gas Tungsten Arc (GTA) which is a kind of a transfer-type plasma torch, it is difficult to apply it to low temperature region such... more
ABSTRACT Although the LTE assumption is effective to evaluate high temperature region in the arc column in Gas Tungsten Arc (GTA) which is a kind of a transfer-type plasma torch, it is difficult to apply it to low temperature region such as the fringe of the arc column or an electrical sheath due to decrease of collision frequency. Especially, in order to consider the effect of chemical reaction between the arc plasma and the surface of the anode material, non-equilibrium property of the arc plasma should be considered without the LTE assumption, since it is required to understand precise property of the arc plasma close to the anode surface. Therefore, we have developed non-equilibrium simulation model of GTA. In this paper, the reliability of the model was confirmed for comparing the simulation result with the experimental result. Furthermore, it was found that the thickness of non-equilibrium region in case of 150A is approximately 0.3mm near the anode surface and that in case of 50A exceeds 1mm.
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A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets).... more
A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets). 1:0 (pure hydrogen), 3:1 (to simulate decomposed ammonia), 2:1 (to simulate decomposed hydrazine) and 0:1 (pure nitrogen) hydrogen/nitrogen mixtures are chosen as the propellants. Both the gas flow
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The calculation and measurement of the properties of thermal plasmas in mixtures of different gases are reviewed. The calculation of composition, thermodynamic properties and transport coefficients is described. Particular attention is... more
The calculation and measurement of the properties of thermal plasmas in mixtures of different gases are reviewed. The calculation of composition, thermodynamic properties and transport coefficients is described. Particular attention is given to the calculation of diffusion coefficients, which is a significant problem in mixed-gas plasmas. The combined diffusion coefficient formulation is shown to be a useful method for the treatment of diffusion. Computational fluid dynamic modelling of thermal plasmas in gas mixtures is considered, using the examples of demixing in welding arcs, the turbulent mixing of atmospheric air into a plasma jet and a plasma waste destruction process. Diagnostic techniques for mixed-gas plasmas, in particular emission spectroscopy, laser scattering and laser-induced fluorescence, are discussed.
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This review paper presents historical perspectives, recent advances and future directions in the multidisciplinary research field of plasma nanoscience. The current status and future challenges are presented using a three-dimensional... more
This review paper presents historical perspectives, recent advances and future directions in the multidisciplinary research field of plasma nanoscience. The current status and future challenges are presented using a three-dimensional framework. The first and the largest dimension covers the most important classes of nanoscale objects (nanostructures, nanofeatures and nanoassemblies/nanoarchitectures) and materials systems, namely carbon nanotubes, nanofibres, graphene, graphene nanoribbons, graphene nanoflakes, nanodiamond and related carbon-based nanostructures; metal, silicon and other inorganic nanoparticles and nanostructures; soft organic nanomaterials; nano-biomaterials; biological objects and nanoscale plasma etching. In the second dimension, we discuss the most common types of plasmas and plasma reactors used in nanoscale plasma synthesis and processing. These include low-temperature non-equilibrium plasmas at low and high pressures, thermal plasmas, high-pressure microplasmas, plasmas in liquids and plasma-liquid interactions, high-energy-density plasmas, and ionized physical vapour deposition as well as some other plasma-enhanced nanofabrication techniques. In the third dimension, we outline some of the 'Grand Science Challenges' and 'Grand Socio-economic Challenges' to which significant contributions from plasma nanoscience-related research can be expected in the near future. The urgent need for a stronger focus on practical, outcome-oriented research to tackle the grand challenges is emphasized and concisely formulated as from controlled complexity to practical simplicity in solving grand challenges.
Research Interests: Engineering, High Pressure, Carbon, Nanofabrication, Carbon Nanotubes, and 15 moreCarbon Nanotube, Nanoparticles, High Energy Density Physics, Nanotechnology, Physical Vapor Deposition, Nanofiber, Physical sciences, Nanostructures, Nanostructure, Plasma Etching, Thermal Plasma, Three Dimensional, Interaction Design for Energy, Low Temperature, and Low Pressure Boiler
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Pseudomonas aeruginosa ATCC 9027 (DSM1128) is often used as a quality-control strain for sterility and microbial contamination testing and is an important biosurfactant producer. Here, we present the 6.4-Mb draft genome sequence and... more
Pseudomonas aeruginosa ATCC 9027 (DSM1128) is often used as a quality-control strain for sterility and microbial contamination testing and is an important biosurfactant producer. Here, we present the 6.4-Mb draft genome sequence and highlight some genomic differences to its closest relative, P. aeruginosa strain PA7.
Two main methods have been used to calculate the transport properties of two-temperature (2-T) plasmas in local chemical equilibrium: the method of Devoto (method B), in which coupling between electrons and heavy species is neglected, and... more
Two main methods have been used to calculate the transport properties of two-temperature (2-T) plasmas in local chemical equilibrium: the method of Devoto (method B), in which coupling between electrons and heavy species is neglected, and the method of Rat et al (method C), in which coupling is included at the cost of a considerable increase in complexity. A new method (method A) has recently been developed, based on the modified Chapman–Enskog solution of the species Boltzmann equations. This method retains coupling between electrons and heavy species by including the electron–heavy-species collision term in the heavy-species Boltzmann equation. In this paper, the properties of 2-T argon plasmas calculated using the three methods are compared. The viscosity, electrical conductivity and translational thermal conductivity obtained using all three methods are very similar. method B does not allow a complete set of species diffusion coefficient to be obtained. It is shown that such a s...
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Microwave energy at 2.45 GHz was applied to a mixture of exhaust gases from a petrol engine at atmospheric pressure. It was found that by pulsing the microwave energy with a 50% duty cycle, the average power required to sustain a... more
Microwave energy at 2.45 GHz was applied to a mixture of exhaust gases from a petrol engine at atmospheric pressure. It was found that by pulsing the microwave energy with a 50% duty cycle, the average power required to sustain a microwave-induced plasma discharge was decreased by about 40%. The ratio of absorbed to incident power was unaffected. These findings were confirmed for pulse frequencies from 10 to 300 Hz.
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Relative radial concentration profiles of atomic hydrogen in an atmospheric-pressure argon-hydrogen free-burning 200-A arc discharge were measured using laser-induced fluorescence by two-photon excitation of the ground state of atomic... more
Relative radial concentration profiles of atomic hydrogen in an atmospheric-pressure argon-hydrogen free-burning 200-A arc discharge were measured using laser-induced fluorescence by two-photon excitation of the ground state of atomic hydrogen. Radial profiles are presented for three axial locations. A comparison between the measured profiles and profiles calculated using a diffusion model that considers demixing processes is made. The measured profiles decrease less rapidly with increasing radius than the calculated profiles, suggesting, in agreement with calculations, that the diffusion rate of atomic hydrogen is greater than the recombination rate. Consequently, local chemical equilibrium is not maintained at larger radii in the arc.
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The generation of heat in a group of nanoparticles attached to a flat surface due to absorption of light was studied. The reflection of light by the substrate was specifically considered and it was found that, depending on the incident... more
The generation of heat in a group of nanoparticles attached to a flat surface due to absorption of light was studied. The reflection of light by the substrate was specifically considered and it was found that, depending on the incident angle and the polarization of the incident light, the reflected light can strongly affect the absorption efficiency of the nanoparticles.
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ABSTRACT Ammonia was synthesized from nitrogen and hydrogen in a dielectric-barrier discharge reactor packed with glass spheres and MgO pellets at atmospheric pressure. The addition of argon to nitrogen and hydrogen, and increasing the... more
ABSTRACT Ammonia was synthesized from nitrogen and hydrogen in a dielectric-barrier discharge reactor packed with glass spheres and MgO pellets at atmospheric pressure. The addition of argon to nitrogen and hydrogen, and increasing the peak voltage, led to increases in discharge power and uniformity, gas temperature, and the fraction of hydrogen converted to ammonia.
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Abstract The diffuse reflectance of films formed by the deposition of gold nanoparticles on a porous polymer substrate is investigated. Measured reflectances are compared with those calculated using a two-flux model of radiative transfer,... more
Abstract The diffuse reflectance of films formed by the deposition of gold nanoparticles on a porous polymer substrate is investigated. Measured reflectances are compared with those calculated using a two-flux model of radiative transfer, modified to take into account the ...
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ABSTRACT In order to clarify fume formation mechanism in arc welding, quantitative investigation based on understanding of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of... more
ABSTRACT In order to clarify fume formation mechanism in arc welding, quantitative investigation based on understanding of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of heterogeneous condensation model, homogeneous nucleation model and coagulation model considering Brownian force and Coulomb force as driving force of particle has been developed and coupled with a GMA welding model. A series of processes from evaporation of metal vapor to fume formation from the metal vapor was totally investigated by employing this simulation model. This study aims to visualize the fume formation process and clarify the fume formation mechanism theoretically through numerical analysis. Furthermore, the reliability of the simulation model was also evaluated through comparison of the simulation result with experimental result. As a result, it was also clarified that most part of the fume was produced in downstream region of the arc originating from the metal vapor evaporated mainly from the droplet. This kind of fume was constituted of particles with size of several nm. On the other hand, if the metal transfer becomes unstable and the metal vapor near the droplet diffuses directly toward the surroundings of the arc not getting on the plasma flow, the sizes of particles reach 1 μm.
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This paper mainly focuses on the influence of three kinds of media: air, air-10%PA (Nylon) and air-10% POM (polyoxymethylene) on low-voltage circuit breaker arcs. A three-dimensional (3-D) model of arc motion under the effect of external... more
This paper mainly focuses on the influence of three kinds of media: air, air-10%PA (Nylon) and air-10% POM (polyoxymethylene) on low-voltage circuit breaker arcs. A three-dimensional (3-D) model of arc motion under the effect of external magnetic field is built based on magnetohydrodynamics (MHD) equations. By adopting the commercial computational fluid dynamics (CFD) package based on the control-volume method, the
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The application of thermochemical modeling, chemical kinetic modeling, and computational fluid dynamic modeling to waste destruction by thermal plasmas is considered. Destruction of liquid and gaseous wastes in the PLASCON™ waste... more
The application of thermochemical modeling, chemical kinetic modeling, and computational fluid dynamic modeling to waste destruction by thermal plasmas is considered. Destruction of liquid and gaseous wastes in the PLASCON™ waste destruction process is used as an example. It is demonstrated that thermochemical calculation of the mixing temperature is a useful tool to predict the level to which wastes are
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Thomson scattering measurements have yielded electron temperatures T(e) up to 7000 K greater than the ion temperature in 1 bar thermal plasmas. To account for laser heating of electrons, T(e) was measured as a function of laser pulse... more
Thomson scattering measurements have yielded electron temperatures T(e) up to 7000 K greater than the ion temperature in 1 bar thermal plasmas. To account for laser heating of electrons, T(e) was measured as a function of laser pulse energy, and an unperturbed T(e) obtained by linear extrapolation to zero pulse energy. It is shown that the absorption of laser energy by the electrons, and the cooling of the electrons by collisions and radiative emission, depend strongly on T(e). Considering all these processes gives T(e) values that are in much closer agreement with the ion temperature.
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A number of assessments of electron temperatures in atmospheric-pressure arc plasmas using Thomson scattering of laser light have recently been published. However, in this method, the electron temperature is perturbed due to strong... more
A number of assessments of electron temperatures in atmospheric-pressure arc plasmas using Thomson scattering of laser light have recently been published. However, in this method, the electron temperature is perturbed due to strong heating of the electrons by the incident laser beam. This heating was taken into account by measuring the electron temperature as a function of the laser pulse energy, and linearly extrapolating the results to zero pulse energy to obtain an unperturbed electron temperature. In the present paper, calculations show that the laser heating process has a highly nonlinear dependence on laser power, and that the usual linear extrapolation leads to an overestimate of the electron temperature, typically by 5000 K. The nonlinearity occurs due to the strong dependence on electron temperature of the absorption of laser energy and of the collisional and radiative cooling of the heated electrons. There are further problems in deriving accurate electron temperatures from laser scattering due to necessary averages that have to be made over the duration of the laser pulse and over the finite volume from which laser light is scattered. These problems are particularly acute in measurements in which the laser beam is defocused in order to minimize laser heating; this can lead to the derivation of electron temperatures that are significantly greater than those existing anywhere in the scattering volume. It was concluded from the earlier Thomson scattering measurements that there were significant deviations from equilibrium between the electron and heavy-particle temperatures at the center of arc plasmas of industrial interest. The present calculations indicate that such deviations are only of the order of 1000 K in 20 000 K, so that the usual approximation that arc plasmas are approximately in local thermodynamic equilibrium still applies.
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The generation of heat by clusters and arrays of gold nanoparticles under illumination is investigated theoretically. The nanoparticles are embedded in a homogeneous dielectric medium, and the finite thermal resistance at the interface... more
The generation of heat by clusters and arrays of gold nanoparticles under illumination is investigated theoretically. The nanoparticles are embedded in a homogeneous dielectric medium, and the finite thermal resistance at the interface between the nanoparticle and the medium is taken into account. An analytic solution is derived for the case of a single nanoparticle. The T-matrix method is used to calculate the energy absorption efficiency of groups of nanoparticles, taking into account their optical interactions. Heat transfer equations are developed that take into account thermal interactions between nanoparticles. The equations are solved numerically using the finite element software COMSOL. Periodic boundary conditions are applied to treat the thermal interactions between the nanoparticles for arrays of nanoparticles. Results are presented for illumination by a standard xenon flash lamp. The thermal resistance at the nanoparticle-medium interface is found to strongly influence the nanoparticle temperature, but to have negligible influence on the temperature of the dielectric medium after a few tens of nanoseconds of exposure to the flash lamp pulse. Optical interactions are found to be important if particle centres are separated by about twice the particle diameter or less. Thermal interactions between nanoparticles via the medium are found to be the dominant factor in determining the temperature increase in the dielectric medium. The maximum temperature increase is proportional to the volume fraction of the nanoparticles in the medium.
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ABSTRACT The development of a three-dimensional computational model of gas–metal arc welding is described. The wire electrode, arc plasma and weld pool are included in the computational domain self-consistently. The model takes into... more
ABSTRACT The development of a three-dimensional computational model of gas–metal arc welding is described. The wire electrode, arc plasma and weld pool are included in the computational domain self-consistently. The model takes into account the motion of the electrode, flow in the weld pool, deformation of the weld-pool surface and the influence of metal droplet transfer. Results are presented for welding of an aluminium alloy. The current density distribution at the interface between the arc and the weld pool is strongly dependent on the surface profile of the weld pool. This in turn affects the temperature distribution in the weld pool. The momentum transferred by the droplet affects the direction of flow in the weld pool, and together with the energy transfer, increases the weld-pool depth. The results demonstrate the importance of including the arc plasma in the computational domain. Fair agreement is found between a measured weld profile and the predictions of the model. Inclusion of the influence of metal vapour in the model is expected to improve the agreement.
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